Devices in which a reagent is added to a sample in a reaction vessel, and the thus-obtained gaseous measuring sample, e.g., a volatile hydride of a looked for element, is transmitted into a heatable measuring cell, are known in different forms. Examples of such devices are DE-PS 26 27 255, DE-PS 26 40 285, DE-AS 27 18 381, DE-OS 27 29 744, and DE-AS 27 35 281. Further devices of this type are shown in DE-AS 28 51 058, DE-PS 27 48 685, DE-PS 32 26 234, and DE-PS 32 26 235. DE-OS 35 25 166 shows an arrangement in which volatile hydrides are supplied to a plasma emission device or to a measuring cell wherein, by means of the sample and reagent pumps, the sample and the reagent can be alternatively rapidly united or continual liquid currents can be generated over a relatively long measuring period of time by the continuous operation with slow forward displacement of the pump pistons.
DE-AS 29 43 092 describes, with regard to the prior art, a method by which mercury is expelled from a sample by means of a reducing agent. For determining small quantities of mercury, the mercury vapor obtained by the reduction is guided for enrichment over silver or gold wool. Thereby, the mercury forms an amalgam with the silver and the gold, respectively. The mercury, thus bound as amalgam, can then be re-expelled through heating and guided into a measuring cell. A higher concentration of mercury is thus obtained in the measuring cell than would be obtained with the direct measurement of the mercury vapor expelled by the reducing agent from the sample solution. Thus, the sensitivity can be increased by approximately the factor 10.
According to the teachings of DE-AS 29 43 092, the mercury is not separated by expelling mercury vapor from a sample solution by means of a reducing agent but rather by the electrolysis of the sample solution.
DE-OS 37 23 178 shows a flow injection device wherein a flow of reagent to a measuring device is generated by means of a peristaltic pump. Through a reversing valve having a loop of tubing located in a conduit of a carrier liquid, a sample liquid contained in the look of tubing is introduced into the flow of reagent. The reagent is a reducing agent which produces, out of hydridizing components of the sample liquid such as arsenic, corresponding volatile hydrides which are separated from the liquid flow in a gas separator and guided into a heated measuring cell. The gas separator forms herein the "reaction vessel".
German Published Patent Application No. 3,344,914 describes an apparatus for analyzing a liquid containing constituents which form volatile compounds, by means of a physical analyzing device. A reaction vessel comprises at its lower end, an outlet valve. A flushing valve which is connected to a flushing liquid reservoir is located at the upper end of the reaction vessel. A metering conduit provided with an inlet valve opens into the lower half of the reaction vessel. Via the metering conduit, sample liquid is conveyed from sample receptacles into the reaction vessel by means of a peristaltic pump. The sample receptacles are present on a turntable. The valves are controlled by programmed control means in a manner such that, following each analysis, the reaction vessel is emptied and then flushed using the flushing liquid; thereafter, a further sample is supplied and reagent is added thereto.
PCT Published Application No. WO 88/08527 describes a graphite tube furnace for atomizing liquid samples. A liquid sample is introduced into a graphite tube through an inlet opening. Atomization is effected by passing a strong electric current through the graphite tube. During this operation, an inert gas flow is flown past the graphite tube. Means are provided for infeeding reactive gases into the chamber defined by the graphite tube. In this manner, reducing, oxidizing, or neutral environmental conditions can be created within the chamber, or there can also be varied the pH-value.
In the textbook entitled "Atomic Absorption Spectrometry", by Welz, published by Verlag Chemie 1983, pages 71 to 84, there are described analytical methods of producing volatile hydrides from liquid samples by the addition of reagents. It is described in which manner these hydrides are then atomized and the process can be automated.
A publication by Mertens and Althaus in "Fresenius Zeitschrift fur analytische Chemie", vol. 316, 1983, pages 696 to 698, describes a method of determining mercury by means of the amalgam technique, using hydroxylammonium chloride and sodium borohydride or tin (II) chloride. Also in this method, a reducing agent is added to a liquid sample in a reaction vessel. The thus formed mercury vapor is flushed by means of a nitrogen current through a wash flask and an aerosol trap and flows over a gold platinum wire. The mercury is enriched thereat by amalgam formation. The enriched mercury is driven off by the application of heat and determined in a measuring cuvette by atomic absorption spectroscopy.
A publication by Messerschmidt and Tolg in "Fresenius Zeitschrift fur analytische Chemie", vol. 327, 1987, pages 233 to 234, describes the determination of selenium. Therefore, selenium, which is present in a liquid sample, is converted into a volatile hydride by sodium borohydride and passed through an adsorption tube by means of a helium current. The adsorption tube can be cooled by liquid nitrogen whereby selenium hydride is adsorbed at an adsorbent. After such enrichment, the selenium hydride can be driven off by rapidly heating the adsorption tube and passed into the measuring cuvette of an atomic absorption spectrometer.
Austrian Patent No. 350,508 relates to a method of quantitatively determining mercury in organic materials. A reagent is infed into a reaction vessel containing the sample by means of a peristaltic pump. Also, a carrier gas stream is infed into this reaction vessel. The thus formed mercury vapor is passed to an adsorption tube via a drying tube. Therein, the mercury is enriched and ultimately driven off by heating the adsorption tube and passed to a measuring cuvette.
German Published Patent Application No. 3,044,627 relates to an apparatus for infeeding samples into a graphite tube for flameless atomic absorption spectroscopy. A sample is applied to a crucible-shaped sample carrier which can be introduced into the graphite tube. This sample carrier is subject to contactless heating for drying and ashing the sample by heating means disposed exterior of the sample carrier.